This invention relates to a unique mooring system for a particular semisubmersible tender that facilitates the servicing of off shore oil and natural gas production platforms.
The present invention specifically relates to the method and apparatus of the mooring system for a semisubmersible tender which tender can be secured to different types of production platforms, such as a tension leg platform (TLP), a deep draft cassion vessel (SPAR), a fixed platform, a compliant tower, a semisubmersible production vessel, or a floating vessel.
Natural gas and oil production platforms typically lack adequate space for all the drilling equipment needed to safely drill a well and store drilling equipment and materials in an environmentally conscientious manner. Tenders have often been called into service to provide the required space needed on a rig and/or platform after the initial drilling phase of an oil lease and during maintenance of a well. Problems have traditionally existed in that most tenders cannot be kept alongside a platform in a constant spaced relationship during extreme weather because of inadequate mooring systems which do not prevent collision of the tender with the platform.
Specifically, tenders have not been able to remain in a connected capacity while moored and simultaneously avoid the risk of collision while enduring an environmental load of up to a 10 year storm, see for example the inventions of U.S. Pat. Nos. 4,065,934, and 4,156,577, which are hereby incorporated by reference.
It should be noted that most tenders have had to be completely towed away from the production platforms and be disconnected from their moorings when a tropical storm or extreme weather arises, which causes considerable expense to the drilling contractor and/or customer.
Until the existence of this invention as described herein, it has been generally believed to be impossible to safely moor a semisubmersible tender to a floating production platform in water depths exceeding several hundred feet.
The present invention is a mooring system for and method of mooring a semisubmersible tender. A mooring system has long been needed which enables the tender to be kept a constant distance from a production platform while enabling a tender to synchronize to the low and mean movement frequencies of the production platform. The mooring system of the invention permits the tender to sustain an environmental load of wind, current and wave forces of up to a 100-year cyclonic storm (such as a hurricane) in a 100-year extreme weather standby position, and up to a 10-year storm in a tendering position.
The invention relates to a mooring system for a semisubmersible tender for use with a production platform in the initial drilling phase of a well. It is also a mooring system for a tender doing maintenance on a well.
The invention relates to an at least 8-point mooring system for a semisubmersible tender which uses at least 8 anchors; at least 8 mooring lines, with each line consisting of: a first length of steel wire rope secured to each of the anchors; a length of polymer rope secured to each of the first length of steel wire rope; a second length of steel wire rope having a first and second end, and wherein the first end is secured to the length of polymer rope and the second end is secured to the tender. Each mooring line has sufficient elasticity, stiffness and strength to accommodate an environmental load produced by up to a 10-year storm while the tender is moored in the tendering position, and each mooring line has sufficient elasticity, stiffness and strength to withstand an environmental load produced by up to a 100-year extreme weather condition when the tender is moved to a 100-year extreme weather condition standby position. The mooring system enhances the global equilibrium between the production platform""s mooring system and the at least 8 point mooring system usable with the semisubmersible tender.